Hemolytic disease of the newborn (HDN) can occur if the mother is which of the following?

The choice concerning the mother being Rh-negative and the fetus being Rh-positive is correct because hemolytic disease of the newborn (HDN) specifically arises from an incompatibility between maternal and fetal blood types, particularly involving the Rh factor.

In this scenario, when a mother is Rh-negative, she lacks the Rh antigen (D antigen) on her red blood cells. If the fetus is Rh-positive—meaning the fetus has inherited the Rh antigen from the father—this can stimulate an immune response in the mother. During pregnancy or delivery, fetal blood may enter the maternal circulation, exposing the Rh-negative mother to Rh-positive blood. The mother's immune system may then produce antibodies against the Rh antigen, which can cross the placenta in subsequent pregnancies, leading to hemolysis of fetal red blood cells. This condition can lead to serious complications for the newborn, including anemia, jaundice, or even severe fetal distress.

In contrast, the other options do not generate the same risk for HDN. For instance, if the mother is Rh-positive, there is no concern with respect to HDN related to the Rh factor since the mother has the same Rh antigen as her fetus. Similarly, blood group incompatibilities based on ABO typing (as seen in options C